Alternating hardmasks for tight-pitch line formation

ABSTRACT

A method for forming fins includes forming a three-color hardmask fin pattern on a fin base layer. The three-color hardmask fin pattern includes hardmask fins of three mutually selectively etchable compositions. Some of the fins of the first color are etched away with a selective etch that does not remove fins of a second color or a third color and that leaves at least one fin of the first color behind. The fins of the second color are etched away. Fins are etched into the fin base layer by anisotropically etching around remaining fins of the first color and fins of the third color.

BACKGROUND Technical Field

The present invention generally relates to semiconductor fabricationand, more particularly, to the formation of hardmasks in semiconductorfabrication processes.

Description of the Related Art

Fin field effect transistors (FinFETs) and other fin-based devices arefrequently used in semiconductor structures to provide small-scaleintegrated circuit components. As these devices scale down in size,performance can be increased but fabrication becomes more difficult. Inparticular, errors in edge placement, critical dimension, and overlayapproach the size of the structures being fabricated, making itdifficult to accurately form such structures.

One particular challenge in forming fin structures is the selectiveremoval of particular fins. For example, while a series of fins can becreated using, e.g., sidewall image transfer techniques, significanterrors in masking the fins may occur when operating near the limit ofthe lithographic process. Such errors may cause fins neighboring theremoved fin to be damaged or removed entirely.

SUMMARY

A method of forming fins includes forming a three-color hardmask finpattern on a fin base layer. The three-color hardmask fin patternincludes hardmask fins of three mutually selectively etchablecompositions. Some of the fins of the first color are etched away with aselective etch that does not remove fins of a second color or a thirdcolor and that leaves at least one fin of the first color behind. Thefins of the second color are etched away. Fins are etched into the finbase layer by anisotropically etching around remaining fins of the firstcolor and fins of the third color.

A method of forming a three-color hardmask fin pattern includesdepositing a second-color material around fins of a first color. Fins ofthe first color are etched away, leaving gaps. The etch further leavesat least one fin of the first color remaining. Fins of a third color areformed in the gaps.

A method of forming a three-color hardmask fin pattern includes formingfins of a first color on a fin base layer, by forming self-assembledfins on a seed layer, etching away every other self-assembled fin,leaving remaining self-assembled fins having differing heights, andetching down into a layer of first-color material around the remainingself-assembled fins to form fins of a first color. A second-colormaterial is deposited around the fins of the first color. Fins of thefirst color are etched away, leaving gaps. Fins of a third color areformed in the gaps.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description will provide details of preferred embodimentswith reference to the following figures wherein:

FIG. 1 is a cross-sectional diagram of a step in the formation of atri-color hardmask in accordance with one embodiment of the presentinvention;

FIG. 2 is a cross-sectional diagram of a step in the formation of atri-color hardmask in accordance with one embodiment of the presentinvention;

FIG. 3 is a cross-sectional diagram of a step in the formation of atri-color hardmask in accordance with one embodiment of the presentinvention;

FIG. 4 is a cross-sectional diagram of a step in the formation of atri-color hardmask in accordance with one embodiment of the presentinvention;

FIG. 5 is a cross-sectional diagram of a step in the formation of atri-color hardmask in accordance with one embodiment of the presentinvention;

FIG. 6 is a cross-sectional diagram of a step in the formation of atri-color hardmask in accordance with one embodiment of the presentinvention;

FIG. 7 is a cross-sectional diagram of a step in the formation of atri-color hardmask in accordance with one embodiment of the presentinvention;

FIG. 8 is a cross-sectional diagram of a step in the formation of atri-color hardmask in accordance with one embodiment of the presentinvention;

FIG. 9 is a cross-sectional diagram of a step in the formation of atri-color hardmask in accordance with one embodiment of the presentinvention;

FIG. 10 is a cross-sectional diagram of a step in the formation of atri-color hardmask in accordance with one embodiment of the presentinvention;

FIG. 11 is a cross-sectional diagram of a step in the selective etch offins using a tri-color hardmask in accordance with one embodiment of thepresent invention;

FIG. 12 is a cross-sectional diagram of a step in the selective etch offins using a tri-color hardmask in accordance with one embodiment of thepresent invention;

FIG. 13 is a cross-sectional diagram of a step in the selective etch offins using a tri-color hardmask in accordance with one embodiment of thepresent invention;

FIG. 14 is a cross-sectional diagram of a step in the selective etch offins using a tri-color hardmask in accordance with one embodiment of thepresent invention;

FIG. 15 is a cross-sectional diagram of a step in the selective etch offins using a tri-color hardmask in accordance with one embodiment of thepresent invention;

FIG. 16 is a cross-sectional diagram of a step in the selective etch offins using a tri-color hardmask in accordance with one embodiment of thepresent invention;

FIG. 17 is a block/flow diagram of a method of a forming tri-colorhardmask in accordance with one embodiment of the present invention; and

FIG. 18 is a block/flow diagram of a method of etching fins using atri-color hardmask in accordance with one embodiment of the presentinvention.

DETAILED DESCRIPTION

Embodiments of the present invention provide a hardmask fabricationprocess that may be used for fin formation in semiconductor fabrication.The present embodiment forms hardmask fins of three differentcompositions that have mutual etch selectivity, such that a spacingbetween fins of the same type is large enough that lithographic maskingerrors will not interfere when selectively removing fins. This providesa tri-color alternating hardmask, where the three different “colors”represent the three different fin hardmask composition. Thus the term“color” is defined herein to refer to one particular hardmaskcomposition.

The present disclosure therefore refers to “first-color,”“second-color,” and “third-color” materials and fins. Each of these“colors” can be etched selectively to the other two, making it possibleto remove a fin of one color without damaging nearby fins of a differentcolor.

Referring now to FIG. 1, a cross-sectional diagram of a step in formingtri-color alternating hardmask is shown. A layer of fin base material104 is formed on a semiconductor substrate 102. The semiconductorsubstrate 102 may be a bulk-semiconductor substrate. In one example, thebulk-semiconductor substrate may be a silicon-containing material.Illustrative examples of silicon-containing materials suitable for thebulk-semiconductor substrate include, but are not limited to, silicon,silicon germanium, silicon germanium carbide, silicon carbide,polysilicon, epitaxial silicon, amorphous silicon, and multi-layersthereof. Although silicon is the predominantly used semiconductormaterial in wafer fabrication, alternative semiconductor materials canbe employed, such as, but not limited to, germanium, gallium arsenide,gallium nitride, cadmium telluride, and zinc selenide. Although notdepicted in the present figures, the semiconductor substrate 102 mayalso be a semiconductor on insulator (SOI) substrate.

The fin base material 104 may be any appropriate material that may beused as a hardmask for the eventual formation of semiconductor fins inthe semiconductor substrate 102. In one embodiment, it is contemplatedthat the layer of fin base material 104 may have a thickness of about 40nm. It is specifically contemplated that silicon nitride may be used forthe fin base material 104, but it should be understood that anyappropriate hardmask material having etch selectivity with theunderlying semiconductor and the three tri-color hardmask materials maybe used. As used herein, the term “selective” in reference to a materialremoval process denotes that the rate of material removal for a firstmaterial is greater than the rate of removal for at least anothermaterial of the structure to which the material removal process is beingapplied.

A layer of first-color hardmask material 106 is formed on the fin basematerial 104. It is specifically contemplated that the first-colorhardmask material 106 may be formed from amorphous silicon, but anyappropriate hardmask material having etch selectivity with the fin basematerial 104 and the other two tri-color hardmask materials may be usedinstead. In one embodiment the layer of first-color hardmask material106 may have a thickness of about 20 nm.

A stack of layers is formed on top of the layer of first-color hardmaskmaterial 106. In particular, a first stack layer 108 is formed on thelayer of first-color hardmask material 106 and may be formed from thesame material as the fin base material 104 or any other appropriatematerial. In one embodiment the first stack layer 108 may have athickness of about 5 nm. A second stack layer 110 is formed on the firststack layer 108. It is specifically contemplated that the second stacklayer 110 may be formed from a dielectric material such as silicondioxide and may have a thickness of about 10 nm.

A thin seed layer of polymer material 112 is formed on the stack. It isspecifically contemplated that the seed layer 112 may be formed from,e.g., cross-linkable polystyrene, though it should be understood thatother materials may be selected instead. The seed layer 112 is selectedfor its ability to guide later self-assembly of block copolymers (BCPs).In particular, seed material should match one of the two chains of theblock copolymer system. For example, if a polystyrene/poly(methylmethacrylate) (PMMA) block copolymer is used, the seed layer 112 may becross-linkable polystyrene. If a polystyrene/polyvinyl phenol (PVP)block copolymer is used, then the seed layer 112 may be cross-linkablePVP. In one particular embodiment, the seed layer 112 may be formed to athickness between about 5 nm and about 8 nm, though it should beunderstood that greater or lesser thicknesses are also contemplated.

A set of fins 116 is formed on the seed layer 112. It is specificallycontemplated that the fins 116 may be formed from a photoresist. Theresist pattern of fins is formed at a pitch that is twice the naturalperiod of the BCPs, which determines the ultimate fin pitch. Forexample, if fins having a pitch of 20 nm are ultimately needed, the fins116 are formed at a pitch of 40 nm.

Referring now to FIG. 2, a cross-sectional diagram of a step in formingtri-color alternating hardmask is shown. The fins 116 are used as a maskto etch the seed layer 112 and the second stack layer 110. A directionaletch, such as a reactive ion etch (RIE) may be used. Remaining maskmaterial 116 after etch is then stripped by solvent to keep 204 intact.Portions of the seed layer 204 remain on fins of the second stackmaterial 202.

RIE is a form of plasma etching in which, during etching, the surface tobe etched is placed on a radio-frequency powered electrode. Moreover,during RIE the surface to be etched takes on a potential thataccelerates the etching species extracted from plasma toward thesurface, in which the chemical etching reaction is taking place in thedirection normal to the surface. Other examples of anisotropic etchingthat can be used at this point include ion beam etching, plasma etchingor laser ablation.

Referring now to FIG. 3, a cross-sectional diagram of a step in formingtri-color alternating hardmask is shown. A brush polymer layer 302 isapplied over the first stack layer 108, the second stack material 202,and the seed layer 204. The brush polymer may be a linear polymer with afunctional group at the chain end that bonds with the underlyingsubstrates except material 204. Brush material 302 may be depositedusing, e.g., spin coating. Limited by only one functional group perchain, a monolayer of brush is bonded to 108 and the sidewall of 202while the excess brush can be rinsed away using solvents. The resultingthickness of the brush polymer layer 302 depends on the molecular sizeof the polymer, which is typically in the range of 2-10 nm. The patterncomposed of 202, 204, and 302 is referred to as the guiding pattern fordirected self-assembly. The brush polymer itself can be a randomcopolymer of the constituents of the block copolymer. For example, apolymer (styrene-random-MMA)-“end group” brush can be used forpolystyrene-PMMA block copolymers.

Referring now to FIG. 4, a cross-sectional diagram of a step in formingtri-color alternating hardmask is shown. A layer of block copolymers(BCP) is spin-coated over the guiding pattern and annealed between about200 and about 280° C. for between about 5 and 100 minutes under nitrogenenvironment to promote the self-assembly process. This directedself-assembly (DSA) process of the BCPs will result in micro-domains402, which will align to 204, 404 and 406. A BCP material used in thiscase is a linear polymer chain with two blocks of chemically distinctpolymers covalently bonded together. In one specific example, theself-assembling BCP material may have one block that is polystyrene,e.g., forming fins 402 and 406, and one block that is poly(methylmethacrylate) (PMMA), e.g., forming fins 404.

The lengths of the polymer chains can be selected to producemicro-domains with pitch between about 10 nm and about 200 nm. In thiscase, it is specifically contemplated that the self-assembling materialmay have halves of equal length of about 5 nm each, forming a chain witha total length of about 10 nm. When the chains self-assemble, with likeends facing one another, the resulting fins of each material are about,e.g., 10 nm in width. The resulting alternating fin configuration hasfin pitch of half the original fin pitch on the guiding pattern. Forexample, if the original resist pattern 116 were formed with a fin pitchof about 40 nm, the fins of first DSA material and second DSA materialhave a respective fin pitch of about 20 nm.

Referring now to FIG. 5, a cross-sectional diagram of a step in formingtri-color alternating hardmask is shown. The fins of second BCP block404 are removed by selective etching, leaving gaps 504 between the finsof first DSA material 402/406. The etch selectively removes the secondDSA material 404 with only partial consumption of the first DSA material402/406 and also etches down into the brushed-on polymer layer 302.Depending on the etch process chosen, selectivity between 404 and402/406 is about or greater than 2.

Referring now to FIG. 6, a cross-sectional diagram of a step in formingtri-color alternating hardmask is shown. Using the fins of first DSAmaterial 402/406 as a mask, the layer of first-color hardmask material106 is etched down. A first breakthrough etch, such as RIE,anisotropically etches the material of the first stack layer 108.Because 402/406 domains have a material-controlled, uniform dimension,any irregularities in the caps of second stack material 202 can betrimmed and rectified during the breakthrough etch. A second anisotropicetch, such as RIE, removes material from the layer of first-colorhardmask material 106, forming fins 604 with caps of the first stackmaterial 602. Caps of the second stack material 202 remain onalternating fins, providing fins of alternating heights.

Referring now to FIG. 7, a cross-sectional diagram of a step in formingtri-color alternating hardmask is shown. An organic planarizing layer(OPL) 702 is deposited onto the surface and recessed down below theheight of the caps of second stack material 202 but above the height ofthe caps of first stack material 602. In one embodiment, the OPL 702 maybe formed from, e.g., spin-on carbon that forms an amorphous-like carbonstructure, but any appropriate planarization material may be usedinstead. The OPL 702 is formed as a second-color hardmask material thathas etch selectivity with the fin base material 104, the fins offirst-color hardmask material 604, and a third-color hardmask material.

Referring now to FIG. 8, a cross-sectional diagram of a step in formingtri-color alternating hardmask is shown. The caps of second stackmaterial 202 are removed selectively using, e.g., a buffered oxide etch,and the exposed caps of the second stack material 602 are removed by aselective etch that leaves the OPL 702 undamaged. Exposed fins 604 arethen removed by a selective etch, leaving behind those fins 604 that areprotected by the OPL 702. Gaps 802 remain between regions of the OPL702.

Referring now to FIG. 9, a cross-sectional diagram of a step in formingtri-color alternating hardmask is shown. The gaps 802 are filled with athird-color hardmask material to form fins 902. The third-color hardmaskmaterial may be, for example, silicon dioxide and may be depositedusing, e.g., atomic layer deposition (ALD), spin-on deposition, orflowable deposition. Alternatively, the third-color hardmask materialmay be any appropriate material that has etch selectivity with the fins(the first-color hardmask material) 604, the OPL (the second-colorhardmask material) 702, and the base fin material 104.

Referring now to FIG. 10, a cross-sectional diagram of a step in formingtri-color alternating hardmask is shown. The OPL 702 is recessed belowthe height of the fin caps of first stack material 602 by chemicalmechanical planarization (CMP) or by RIE, separating the OPL 702 intofins of second-color hardmask material 1002. The result is a series offins which can be selectively etched with respect to their neighbors. Inparticular, the fins of first-color hardmask material 604 and the finsof third-color hardmask material 902 have a pitch to their closestneighbor of the same material that is the same as the pitch of theoriginal fins 116 (e.g., 40 nm). Thus, a mask can be reliably formed forthe removal of one fin without affecting its direct neighbors.

Referring now to FIG. 11, a cross-sectional diagram of a step inselectively removing a fin is shown. An mask 1104 is formed, leavingexposed at least one fin 1102. It should be noted that the mask 1104 mayexpose neighboring fins as well, as long as those fins are not formedfrom the same material as the selected fin 1102. The mask 1104 may beformed by, e.g., chemical vapor deposition, physical vapor deposition,ALD, spin-on deposition, gas cluster ion beam (GCIB) deposition, or anyother appropriate deposition process.

CVD is a deposition process in which a deposited species is formed as aresult of chemical reaction between gaseous reactants at greater thanroom temperature (e.g., from about 25° C. about 900° C.). The solidproduct of the reaction is deposited on the surface on which a film,coating, or layer of the solid product is to be formed. Variations ofCVD processes include, but are not limited to, Atmospheric Pressure CVD(APCVD), Low Pressure CVD (LPCVD), Plasma Enhanced CVD (PECVD), andMetal-Organic CVD (MOCVD) and combinations thereof may also be employed.In alternative embodiments that use PVD, a sputtering apparatus mayinclude direct-current diode systems, radio frequency sputtering,magnetron sputtering, or ionized metal plasma sputtering. In alternativeembodiments that use ALD, chemical precursors react with the surface ofa material one at a time to deposit a thin film on the surface. Inalternative embodiments that use GCIB deposition, a high-pressure gas isallowed to expand in a vacuum, subsequently condensing into clusters.The clusters can be ionized and directed onto a surface, providing ahighly anisotropic deposition.

Referring now to FIG. 12, a cross-sectional diagram of a step inselectively removing a fin is shown. The fin 1102 is etched away usingany appropriate isotropic or anisotropic etch. Because the neighboringfin have etch selectivity with the selected fin 1102, they are notaffected by the removal of the selected fin 1102.

Referring now to FIG. 13, a cross-sectional diagram of a step inselectively preserving a fin is shown. In this example, a mask 1302 isformed over a fin of a particular color to be preserved. The other finsof the first-color hardmask material 604 remain uncovered.

Referring now to FIG. 14, a cross-sectional diagram of a step inselectively preserving a fin is shown. Those fins 604 that are notcovered by the mask 1302 are etched away using any appropriate etch.Because the pitch between the fins 604 is large, there is little risk ofthe mask 1302 covering an unintended fin and preventing such a fin frombeing removed.

Referring now to FIG. 15, a cross-sectional diagram of a step in formingsemiconductor fins is shown. The remaining mask 1302 and the fins of thesecond-color hardmask material 1002 are removed by any appropriateisotropic or anisotropic etch process. The selected fins of first-colorhardmask material 604 and fins of third-color hardmask material 902remain on the fin base material 104.

Referring now to FIG. 16, a cross-sectional diagram of a step in formingsemiconductor fins is shown. The remaining first-color fins 604 andthird-color fins 902 are used as masks to etch the fin base material104, producing a set of hardmask fins 1602. An appropriate directionaletch such as RIE may be used, stopping on the underlying semiconductorsubstrate 102. The fins 1602 may be used directly in subsequentprocessing steps or may, alternatively, be used to form further fins inthe semiconductor substrate 102 for, e.g., fin field effect transistors(FinFETs).

It is to be understood that aspects of the present invention will bedescribed in terms of a given illustrative architecture; however, otherarchitectures, structures, substrate materials and process features andsteps can be varied within the scope of aspects of the presentinvention.

It will also be understood that when an element such as a layer, regionor substrate is referred to as being “on” or “over” another element, itcan be directly on the other element or intervening elements can also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements can be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

The present embodiments can include a design for an integrated circuitchip, which can be created in a graphical computer programming language,and stored in a computer storage medium (such as a disk, tape, physicalhard drive, or virtual hard drive such as in a storage access network).If the designer does not fabricate chips or the photolithographic masksused to fabricate chips, the designer can transmit the resulting designby physical means (e.g., by providing a copy of the storage mediumstoring the design) or electronically (e.g., through the Internet) tosuch entities, directly or indirectly. The stored design is thenconverted into the appropriate format (e.g., GDSII) for the fabricationof photolithographic masks, which typically include multiple copies ofthe chip design in question that are to be formed on a wafer. Thephotolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

Methods as described herein can be used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case, the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case, the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

It should also be understood that material compounds will be describedin terms of listed elements, e.g., SiGe. These compounds includedifferent proportions of the elements within the compound, e.g., SiGeincludes Si_(x)Ge_(1-x) where x is less than or equal to 1, etc. Inaddition, other elements can be included in the compound and stillfunction in accordance with the present principles. The compounds withadditional elements will be referred to herein as alloys.

Reference in the specification to “one embodiment” or “an embodiment”,as well as other variations thereof, means that a particular feature,structure, characteristic, and so forth described in connection with theembodiment is included in at least one embodiment. Thus, the appearancesof the phrase “in one embodiment” or “in an embodiment”, as well anyother variations, appearing in various places throughout thespecification are not necessarily all referring to the same embodiment.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This can be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises,” “comprising,” “includes” and/or “including,” used herein,specify the presence of stated features, integers, steps, operations,elements and/or components, but do not preclude the presence or additionof one or more other features, integers, steps, operations, elements,components and/or groups thereof.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like, can be used herein for ease of description todescribe one element's or feature's relationship to another element(s)or feature(s) as illustrated in the FIGS. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the FIGS. For example, if the device in theFIGS. is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the term “below” can encompass both an orientation ofabove and below. The device can be otherwise oriented (rotated 90degrees or at other orientations), and the spatially relativedescriptors used herein can be interpreted accordingly. In addition, itwill also be understood that when a layer is referred to as being“between” two layers, it can be the only layer between the two layers,or one or more intervening layers can also be present.

It will be understood that, although the terms first, second, etc. canbe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another element. Thus, a first element discussed belowcould be termed a second element without departing from the scope of thepresent concept.

Referring now to FIG. 17, a method of forming three-color hardmask finsis shown. Block 1702 forms photoresist fins 116 on a stack of layers.The stack of layers is described in detail above with respect to FIG. 1.Block 1704 etches photoresist fins into, e.g., a seed layer 114 and anoxide layer 112, creating islands 202 with seed layers 204 on top ofthem. Block 1706 forms a monolayer of polymer brush material 302 on thestack between the islands 202.

Block 1708 forms alternating, self-assembled fins 402, 404, and 406 fromthe guiding pattern, using molecular chains that have one block that isattracted by the seed layer 204 and one block that sits on brushmaterial 302. Block 1710 then removes one type of the fins (particularlyfins 404) using a selective etch process. Block 1712 etches down into afirst-color hardmask material 106 to form first-color fins 604.

Block 1714 forms second-color hardmask material (e.g., OPL 702) in thegaps between the first-color fins 604. Block 1716 then recesses thesecond-color hardmask material down below the height of every otherfirst-color fin, such that the second-color hardmask material has aheight below the height of half of the first-color fins 604 and abovethe height of the other half of the first color fins 604.

Block 1718 removes the exposed first-color fins using any appropriateetch to form gaps 802. Block 1720 forms third-color hardmask material inthe gaps 802. This material may be deposited by any appropriatedeposition process and then polished down using, e.g., chemicalmechanical planarization. CMP is performed using, e.g., a chemical orgranular slurry and mechanical force to gradually remove upper layers ofthe device. The slurry may be formulated to be unable to dissolve, forexample, the work function metal layer material, resulting in the CMPprocess's inability to proceed any farther than that layer.

Block 1722 recesses the second-color material below the height of allthe first-color fins 604. The result is three sets of fins: first-colorfins 604, second-color fins 1002, and third-color fins 902. Each colorof fins has etch selectivity with each of the others, such thatpositioning or size errors in a mask that covers or uncovers aparticular fin are unlikely to affect neighboring fins of the samecolor.

Referring now to FIG. 18, a method of fin formation is shown. Block 1802forms a three-color hardmask fin pattern, for example in the mannerdescribed above with respect to FIG. 17. The hardmask materials of thefins are formed in the sequence of Color ABCBABCBA . . . . Block 1804forms a mask over the three-color hardmask fins, leaving one or morefins exposed. Block 1806 etches away one color of fin in the exposedarea, leaving any other color of fin that may be exposed unharmed. Block1808 removes the mask. One can repeat 1804 to 1808 multiple times toselect different colors of fins to customize before moving onto block1810, which removes all hardmask fins of one of the three colors. In theexamples above, this refers to the second-color fins 604. Block 1812then etches down into an underlying layer (e.g., fin base material 104)to form fins of a uniform material, but with variable spacing.

Having described preferred embodiments of a system and method (which areintended to be illustrative and not limiting), it is noted thatmodifications and variations can be made by persons skilled in the artin light of the above teachings. It is therefore to be understood thatchanges may be made in the particular embodiments disclosed which arewithin the scope of the invention as outlined by the appended claims.Having thus described aspects of the invention, with the details andparticularity required by the patent laws, what is claimed and desiredprotected by Letters Patent is set forth in the appended claims.

What is claimed is:
 1. A method for forming fins, comprising: forming athree-color hardmask fin pattern on a fin base layer, the three-colorhardmask fin pattern comprising hardmask fins of three mutuallyselectively etchable compositions; etching away some of the fins of thefirst color with a selective etch that does not remove fins of a secondcolor or a third color and that leaves at least one fin of the firstcolor behind; etching away the fins of the second color; and etchingfins into the fin base layer by anisotropically etching around remainingfins of the first color and fins of the third color.
 2. The method ofclaim 1, wherein forming the three-color hardmask fin pattern comprises:forming fins of the first color on the fin base layer; depositing asecond-color material around the fins of the first color; etching awayfins of the first color, leaving gaps; and forming fins of a third colorin the gaps.
 3. The method of claim 2, wherein forming fins of the firstcolor comprises: forming self-assembled fins on a seed layer, theself-assembled fins comprising fins of alternating polymer materials;etching away every other self-assembled fin; and etching down into alayer of first-color material around the remaining self-assembled finsto form fins of a first color, leaving remaining fins having differingheights.
 4. The method of claim 3, wherein the fins of the first coloreach comprise a cap of one or more dielectric layers, with differentdielectric layers corresponding to different heights of the fins of thefirst color.
 5. The method of claim 3, wherein forming self-assembledfins comprises applying a block copolymer material having two molecularchains of similar or equal length, wherein one of the two molecularchains is attracted to the seed layer.
 6. The method of claim 5, whereina first chain of the material comprises polystyrene and wherein a secondchain of the material comprises poly(methyl methacrylate).
 7. The methodof claim 3, further comprising etching the second-color material to aheight lower than a height of the tallest remaining self-assembled finsand greater than a height of the shortest remaining self-assembled fins.8. The method of claim 3, wherein etching away fins of the first colorcomprises etching away the fins of the first color having agreater-than-average height.
 9. The method of claim 1, furthercomprising masking a region that covers at least one fin of the firstcolor by forming a mask with a lithographic process having a minimumpitch size that is greater than a fin pitch of the three-color hardmaskfin pattern.
 10. The method of claim 1, further comprising: masking aregion on the three-color hardmask fin pattern, leaving one or more finsof the third color exposed; and etching away all exposed fins of thethird color with a selective etch that does not remove fins of the firstcolor or the second color.
 11. A method of forming a three-colorhardmask fin pattern, comprising: depositing a second-color materialaround fins of a first color; etching away fins of the first color,leaving gaps, wherein the etch further leaves at least one fin of thefirst color remaining; and forming fins of a third color in the gaps.12. The method of claim 11, wherein forming fins of the first colorcomprises: forming self-assembled fins on a seed layer, theself-assembled fins comprising fins of alternating base materials;etching away every other self-assembled fin, leaving remainingself-assembled fins having differing heights; and etching down into alayer of first-color material around the remaining self-assembled finsto form fins of a first color.
 13. The method of claim 12, wherein thefins of the first color each comprise a cap of one or more dielectriclayers, with different dielectric layers corresponding to differentheights of the fins of the first color.
 14. The method of claim 12,wherein forming self-assembled fins comprises applying a material havingtwo molecular chains of similar or equal length, wherein one of the twomolecular chains is attracted to the seed layer.
 15. The method of claim14, wherein a first chain of the material comprises polystyrene andwherein a second chain of the material comprises poly(methylmethacrylate).
 16. The method of claim 12, further comprising etchingthe second-color material to a height lower than a height of the tallestremaining self-assembled fins and greater than a height of the shortestremaining self-assembled fins.
 17. The method of claim 12, whereinetching away fins of the first color comprises etching away the fins ofthe first color having a greater-than-average height.
 18. A method offorming a three-color hardmask fin pattern, comprising: forming fins ofa first color on a fin base layer, by: forming self-assembled fins on aseed layer; etching away every other self-assembled fin, leavingremaining self-assembled fins having differing heights; and etching downinto a layer of first-color material around the remaining self-assembledfins to form fins of a first color; depositing a second-color materialaround the fins of the first color; etching away fins of the firstcolor, leaving gaps; and forming fins of a third color in the gaps. 19.The method of claim 18, further comprising etching the second-colormaterial to a height lower than a height of the tallest remainingself-assembled fins and greater than a height of the shortest remainingself-assembled fins.
 20. The method of claim 18, wherein etching awayfins of the first color comprises etching away the fins of the firstcolor having a greater-than-average height.